Klotho was first identified as an anti-aging gene but Klotho protein has multiple effects including anti-oxidation. Hypoxia induces mitochondrial leak of reactive O2 species (ROS), which can serve as physiologic signals for alveolar growth and remodeling and cell longevity. Conversely, hyperoxia produces excess ROS that induce alveolar degeneration resembling emphysema. Hence, both hypoxia and hyperoxia impose oxidative stress on the lung. Interestingly Klotho deficiency causes a premature aging syndrome with short lifespan, growth retardation, atherosclerosis, organ degeneration and pulmonary emphysema. Mice homozygous for Klotho deletion (KL-/-) die at a young age with widespread abnormalities. Heterozygous mice (KL) develop pulmonary emphysema but are otherwise normal. It is not known if transgenic mice producing excess Klotho protein (Tg-KL) are protected from oxidative damage. We postulate that growth and aging of the lung represent different ends in the spectrum of adaptation to oxidative stress regulated by a shared set of genes, and that Klotho is at the center stage of these pathways. The Aim is to explore the role of Klotho on lung growth and function in animals exposed to different O2 tensions during postnatal life. I will determine the effects of oxidative stress on lung structure and function in mice bearing deficiency or overexpression of the Klotho gene, and test the hypothesis that Klotho deficiency impairs hypoxia-induced lung growth and accelerates hyperoxia- induced lung damage while Klotho overexpression augments hypoxia-induced lung growth and mitigates hyperoxia-induced lung damage. Genetically modified mice and matched controls will be exposed to 13, 21 or 40% O2 for 3 wk, followed by measurement of lung function, ultrastructure, and biomarkers of oxidative damage. Finally, I will test the direct effects of Klotho on the ability of lung epithelial cells to react to oxidative insult in vitro. These studies expand the scope of my training as well as the scientific quest. Drs. Kuro-o and Moe have been investigating the metabolic effects of Klotho on the interaction of aging and disease in multiple organs. They became interested in the lung since it is the only organ in the KL mice that exhibits baseline abnormalities. I will take on the pulmonary part of this Klotho working group in Dr. Moe's laboratory. I will apply what I have learned in my doctorate training as a bioengineer to this new model. I will be in a new environment with greater emphasis on cell and molecular biology in addition to physiology. The results will advance our understanding of fundamental mechanisms that link lung growth and aging, offer new insight into whether manipulation of Klotho production enhances lung growth or protects against degeneration, and lay the foundation for exploring potential uses of Klotho protein, perhaps by inhalational delivery, to augment lung growth or mitigate destruction in the treatment of chronic lung disease. Since Klotho deficiency also exists in humans and Klotho therapy is being intensely studied, this topic has broad biologic and clinical relevance and will be an ideal platform to launch my career as a biomedical researcher.